The present invention relates generally to the field of food processing equipment and, more particularly, to a food processing vat for production and processing of semi-liquid food products, such as cheese. The food processing vat of the present invention is preferably comprised of a closed vessel arranged in a plurality of horizontally orientated, partial frustoconical sections, each section having a separate agitator means which allows maximum product yield to be obtained from the raw materials used.
The use of totally enclosed food processing vats, for the manufacture of many types of cheese and similar semi-liquid food products, is well known in the art. U.S. Pat. Nos. 3,858,855; 4,206,880; 4,938,424 and 5,178,060 are examples of prior art cheese making vats that are fully enclosed. The vats in each of these patents use agitator means, for cutting the coagulum and stirring, that are vertically disposed within a vessel comprised of two partial cylinders. This design is very effective for smaller vessels but becomes less efficient with increases in size due to the need to create vertical movement within the vat contents without generating damagingly high peripheral agitator speeds. In the patents cited above, vertical movement is induced by means of hinged deflector plates which cause maximum turbulence when the agitator is rotated in the stirring direction while maintaining a highly streamlined configuration when the agitator is rotated in the cutting direction.
U.S. Pat. No. 4,108,058 discloses a fully enclosed cheese making vat in the form of a horizontal cylindrical vessel with a single horizontal shaft carrying the combined cutting and stirring paddles. The construction of the agitator paddle results in less damage to the food product and, in the case of cheese, results in minimum release of butterfat and cheese fines into the whey. A major disadvantage of this design is that the whole contents of the vat tend to rotate during cutting and in effect move away from the knife blades. This, together with a very high velocity gradient between the agitator blades near to the shaft and those on the periphery, makes it very difficult to achieve an evenly cut coagulum and can cause problems of product variability.
U.S. Pat. No. 4,989,504 describes a fully enclosed cheese making vat in the form of a plurality of horizontally arranged partial cylindrical sections each with a separate shaft-mounted agitator, such that the distance between agitator shafts is greater than the radius of the swept volume created by the rotation of the agitator. This arrangement is an improvement over the single shaft horizontal vat with regard to rotation of the vat contents during cutting, but the problem of velocity gradient between the agitator paddle near to the shaft and that at the periphery is only slightly reduced. The low agitator speeds that are typically used with this type of food processing vat give rise to very poor agitation adjacent to the agitator shaft and can also cause a significant problem with product congealing around the shaft. The vat construction described in the above U.S. Pat. No. 4,989,504 includes an agitator comprising a series of individual paddles attached to the shafts in staggered rows or in a row wrapped spirally around the shafts. A resultant problem with this arrangement is the extreme difficulty encountered when entering the vat for maintenance or hand cleaning due to the impossibility of parking the agitator paddles in a position that allows easy and safe movement around the inside of the vat.
Although the designs listed above have proved adequate for processing many types of cheese products, modern commercial practice has generated more stringent compositional standards and the requirement for many customized products with special functional properties. Some of these functional properties result in significant production difficulties, especially where it is required to effect partial separation of solid from liquid while maintaining some degree of agitation to prevent the matting together of solid material that takes place if there is no agitation.
In order to achieve the required standard of operation, it would be advantageous to have a horizontal food processing vat that further reduced problems associated with velocity gradients across the agitator, that eliminated the requirement for horizontal shafts running through the center of the swept volumes and that permitted partial separation of solid from liquid during maintained agitation.